The present disclosure is related to illumination sources for portable devices, and more particularly to sources with directable illumination fields.
Modern electronics design and manufacturing has made it possible to provide compact cameras that autonomously handle all aspects of settings and adjustments required to capture properly exposed, properly framed, and properly focused images. Compact digital cameras, point-and-shoot digital cameras, and cell phone and tablet computer cameras (collectively referred to herein as compact cameras) are examples of devices that provide such autonomous settings control. More specifically, such cameras are able to autonomously set aperture opening size (e.g., f-number), aperture opening duration, account for sensor gain (roughly equivalent to ISO film sensitivity), and so on. Such cameras may also identify an image target object in a field of view, and set focus for that target. In general, compact cameras are often intended to provide simple operation for rapid, spontaneous picture taking, and are expected to perform in a wide range of photographic situations, while increases in processing power and software enable the cameras to “understand” more of a scene.
Among the set of situations compact cameras are often designed to perform in are low-light settings, for example indoors, in evening settings, and so on. Usage patterns are predominantly handheld (no tripod) and show an emphasis on snapshots of people. Even with highly sensitive electronic sensors taking the place of film, such settings necessitate using a supplemental light source (referred to as a flash herein) for example to freeze a target and avoid motion blur, to provide desired contrast, and so on. Most compact cameras therefore contain or are provided with a flash unit.
However, to be of use in the widest set of situations (including indoor settings), compact cameras are often designed to provide a relatively wide field of view (with consequent short effective focal length). To accommodate the relatively wide field of view in low-light settings, flash units (often an LED source and today some plastic optics to define its light distribution) for compact cameras are typically designed to illuminate a corresponding wide field of view (wide view angle). Consequently, compact camera flash units illuminates the entire wide angle scene, regardless of the target of the exposure, and even if the camera is zoomed in for a telephoto image. This not only wastes precious energy on generating sufficient light to illuminate the widest possible field of view, but also often results in lower light levels at specific portions of the image frame as well as over-lighting of non-target elements of the image frame. As an example, if a shot is taken at 3× zoom, more than 85% of the flash output will typically go unused. A more efficient use of a light source in compact cameras would provide many benefits, including improved illumination of image target, reduced power consumption, faster image repetition rates, and so on.
While typical compact camera flash sources are fixed in position, with fixed associated optics, some examples exist of flash source with lenses that move in tandem with motion of mechanically controlled zoom and focus imaging optics. In certain applications, these lenses “focus” the output of the flash within the field of the flash exposure. In other examples, an evaluator evaluates a scene to determine an intended image target of the photograph. A lens is then mechanically moved to direct the output of a flash element to the intended image target. Alternatively, the flash element may be tilted relative to the lens to achieve a similar objective. In each of these cases, the “compactness” of the flash system is compromised by the introduction of one or more moveable lenses and lens movement control mechanisms. And only gross position control of the light source (i.e., only control over the entire output of the source) is provided.